1. Field of the Invention
The present invention relates generally to tunable fiber lasers.
2. Description of the Prior Art
Tunable lasers have applications in a wide variety of fields, including optical communications and spectroscopy. For trace gas monitoring, compact tunable (20-30 GHz), wavelength modulatable sources with output powers on the order of approximately 100 μW and linewidths better than 100 MHz are in great demand for wavelength modulation spectroscopy. The availability of high performance erbium-doped fiber amplifiers and pumped lasers allows for tunable fiber lasers. Modulation and switching of optical signals are basic functions in an optical communication system. Through modulation, the information to be communicated is expressed in one or more parameters of a light signal, such as the amplitude, the polarization, the phase or frequency of the field, or of the magnitude or spatial distribution of the power and/or intensity. Through switching, the light signal may be routed through a network of optical nodes and connections.
Precisely wavelength-switchable narrow linewidth laser sources are of great interest for many photonic applications, such as for tuning “on and off” narrow absorption lines in spectroscopic measurements, including the monitoring of resonantly absorbing species in DIAL (differential absorption LIDAR)-type applications. Wavelength-switchable narrow linewidth laser sources are also critically needed for several applications in WDM-based (wavelength division multiplexed) fiber optic communication systems. Key requirements for such multi-wavelength switchable sources for WDM/DWDM systems are: (1) an accurate match with the wavelength channels on the WDM/DWDM ITU grid, (2) an arbitrary set of such channels, (3) a capability for switching reliably to any channel between such a preselected arbitrary set of channels, (4) low crosstalk, and (5) microsecond (or faster) switching speeds.
Past multi-wavelength switchable sources have in general been limited to schemes that are either difficult to scale to a large number of wavelengths, or have relatively slow (millisecond) switching speeds. Laser arrangements such as those found in U.S. Pat. No. 5,504,771 also require the use of stable external “wavelength lockers” to prevent wavelength drift from the FFPs PZT tuning assembly. Multi-frequency lasers based on integrated-optic arrays of DBR and DFB lasers, or SOA (semiconductor optical amplifiers arrays integrated with AWGs (arrayed waveguide gratings) seem to satisfy most of the above requirements. However, these are relatively difficult and expensive to manufacture, particularly in small volumes or for custom applications that may require a combination of numerous arbitrarily-spaced channels on the WDM/DWDM ITU grid.
Therefore, there is still a need for a rapidly switchable multi-wavelength source that is relatively easy to manufacture for any customized set of arbitrary channels on the ITU grid.